The present invention relates to a composition and method for improved gypsum panel foaming. More particularly, the present invention relates to an additive and methods for using an additive for improved gypsum panel foaming. Even more particularly, the present invention relates to compositions and methods utilizing an additive to reduce the impact of hard water on gypsum panel foaming.
Gypsum panels, often referred to as gypsum boards, drywall, wallboard or plasterboard, are typically manufactured by utilizing a faced wall board as used in dry wall construction. A pre-generated foam is added to the panel slurry mix; the foam is generated from a mixture of a foaming agent, air and water in a suitable foam generating apparatus. The foamed gypsum slurry is then deposited onto a moving paper or other substrate supported on a long moving belt. A second substrate may be applied on top of the slurry to constitute the second face of the gypsum board. Next, the sandwich passes through a forming station which determines the width and thickness of the gypsum board. In continuous operation, the gypsum slurry begins to set immediately after the board is formed. Subsequently, the board is cut, dried and bundled into commercially acceptable lengths.
Water mixed to form the foam of the foamed gypsum slurry can vary in hardness. Hard water is typically defined as water that has a relatively high mineral content. In contrast, soft water contains little or no minerals. The content levels typically consist of higher levels of calcium and magnesium metal ions in the form of carbonates, but may include several other metals as well as bicarbonates and sulfates. Descriptions of the hardness of water correspond roughly with the ranges of mineral concentrations:
Mg/L asHardnesscalciumSoft 0-20Moderately Soft20-40Slightly hard40-60Moderately60-80hardHard 80-120Very Hard>120The use of hard water within the foam of the gypsum slurry leads to low volumes of foam produced and board defects related to unwanted coalescence of foam cells once the gypsum is set. In some instances, controlled coalescence to create relatively large foam cells are desired within the foam. In most instances, however, the use of hard water results in unpredictable foaming which can limit line speeds and results in foam cell voids that are much larger than desired. These large foam voids can translate to recovery and/or quality issues, including a reduction in the strength or integrity of the wallboard.
Short term stability of foam added to a gypsum slurry is important in gypsum panel production. Control of this stability controls board core bubble size and impacts gypsum panel strength. To control foam stability, soap compositions can be selected or a foam system blending a binary mixture of soap can be used to increase bubble sizes and strength. It has been determined that a larger bubble size provides greater strength to the finished gypsum panel than smaller bubble sizes. However, excessively large bubble sizes can be detrimental to the quality of the panel. For this reason, it is important when developing a surfactant to take into account other factors which may affect the bubble size in addition to existing soap blends or a foam system to produce blends of stable and unstable soaps to create a foam surfactant. For example, process water can also affect foam stability and in some cases produce a board core with excessively large foam voids, such is the case in the presence of hard water. The present invention provides a composition and methods for using a surfactant composition which provides increased stability and control to the gypsum slurry over a wider range of process conditions. The compositions in accordance with the teachings of the present invention have potential to increase line speed and/or lower board cost during manufacture.
Compositions contemplated for use in embodiments of the invention maximize air entrainment and minimize usage in gypsum panel slurries. In one embodiment, the composition is a surfactant. In other embodiments, the composition is a blend of soaps, including stable soaps, unstable soaps and mixtures thereof. An unstable soap refers to a surfactant of a foaming agent which may produce copious volumes of foam and becomes unstable upon contact with the gypsum slurries. A stable soap refers to a soap developed to maximize air entrainment and minimize usage in gypsum board slurries. Compositions utilizing blends of the stable and the unstable soaps are known, such as in U.S. Pat. No. 5,643,510 issued to Sucech, incorporated herein by reference, which blends compositions of the stable and the unstable soaps for a desired bubble size and shape.
In some cases, other ingredients in the gypsum slurries can cause excessively large voids. For example, the use of hard water as process water can give rise to an excessively large foam core bubble size and soap adjustments (even to 100% stable soap), which are unable to reduce core bubble size to optimum levels. Thus, there are instances in which simply using more of the stable foaming agents (such as surfactants) will not be sufficient to adjust the bubble size. To establish quality and control, productions lines may be resort to slower speed, reformulation and/or higher board manufacturing costs.